Supporting means for acoustical absorbers



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Sept. 16, 1952 o. E. GRUE 2,610,695

SUPPORTING MEANS FOR ACOUSTICAL ABSORBERS Filed Feb. 28. 1.948

INVENTOR: old VX2305, Grue,

i atented Sept. 16,1952

SUPPORTING MEANS FOR ACOUSTICAL ABSORBERS Olav Ebbesen Grue, Copenhagen, Denmark Application February" 28, 1948, SerialNo. 12,081 In Denmark August 27, 1946 2 Claims. (01. 181-33) r The present invention relates to the acousti treatment of rooms for the purpose of damping noise.

,More specifically, the invention relates to sound absorbing units, adapted to be carried near a surface of a room so as to form a sound absorbing system, designed to be used instead of the conventional acoustic tiles or wallboards.

Previous attempts to design sound absorbing units for this-purpose have failed in so far as it has only been proposed either merely to suspend structures of the same type as the traditional wall-boards freely under the ceiling or to attach to the ceiling hollow structures tuned to a certain frequency in the lower frequency range. It is therefore one object of my invention to provide a sound absorber unit which is selfsupporting, has absorbing qualities within a wide frequency range and which is easy to mount. Another object of the invention is to provide a sound absorber unit which, being mounted at a room surface, will give higher absorption than the normal fiat acoustic constructions so as to obtain an improved utilization of the material but without requiring excessive room space in direction perpendicular to the room surface.

I Further objects of my invention are to provide a sound absorber unit and suspension means therefor which are simple and rigid in construction, uncomplicated and inexpensive in production and especially designed for easy packaging and shipment. More specific features by the sound absorbing unit according to the invention will appear from the following specification in connection with the drawings, in which Figures 1 and 2 are twodifferent embodiments of the sound absorbing units in side View,

, Figures 3 and 4 are sections in two different embodiments of sound absorbers,

Figures 5 and 6 show the suspension arrangement in two different embodiments, and

Figure 7 is a modification of Figures 1 and 2.

The units shown in Figures 1 and 2 consist of containers having a surface a, in which are provided apertures, either in form of perforations b, Figure 1, or slots 0, Figure 2. These views are side views and show only the outer shape of the units, illustrating two different patterns of the apertures in the surface of the units. apertures, as will be explained in the following, form passages to the interior of the units and the exemplified two aperture patterns are somewhat conventional.

. The'containers may consist of porous mate-- rial which in itselfis sound absorbing and in These that case the perforations or slots do not need to pass through the walls to the interior, such as indicated in Figure 3, which shows a vertical section through a sound absorber of the type described in side view above. In this embodiment the unit is formed by a casing having a wall 8 which encloses a hollow chamber t. In the exterior surface of the casing, here marked m, are provided apertures b1, distributed all over the surface, similar to the embodiments described above. The wall s itself consists of porous sound absorbing. material, such asmade for instance of wood pulp. The apertures do not penetrate the wall to the interior chambert but terminate blind in the porous material at a distance from the exterior surface (11. By those skilled in the art, a sector of this wall will be found corree sponding to a very common type of acoustic tile having been in public use for many years.

Hence it follows that everything which concerns the wall itself, such as design of material, percentage area of apertures, etc, is well known and can be taken from many a textbook on accuse tics. It will be understood that the size and number of apertures must be sufficient to pro-I vide substantially freepassage of sound waves from the surroundin air through the front sur-. face into the porous material, and that the porous material must have such a porosity asto allow passage of the sound waves and simultaneously. having a considerable .damping effect on the. sound waves passingtherethrough- As mentioned before, the wall may consist. of porous materiaLfor instance of wood pulp, and any conventional materialof the kind normally usedfor wall tiles maybe used, namely material in which wood fibres or the like are held to-' gether by some adhesive which does not influence the porosity. According to the theory of this type of acoustic tile, each aperture defines the neck of a small Helmholtz resonator the bodyof which consists of the space left behind the surface, bounded sidewardly by the bodies of the" neighbor resonators defined by the neighbor apertures and in the conventional wall tile type bounded at the bottom by the surface of the room which mostly coincides with the: rear sur-- -As shown in Figure 2, however, the chamber defined by the wall s has an extension :whi'ch' is large compared with the radial extension of the layer of porous material, or in other words, the wall structure of the casing has opposite parts of the wall which are spaced several times the thickness of the wall structure itself. This is a very important specific feature of the invention which distinguishes the unit from any prior disclosed absorber unit. This requirement must be fulfilled at least at two perpendicular points.

As shown, the wall forms a converging or tapered casing structure. At the widest end of the structure the wall has an edge u surrounding an open side of the chamber 1?. The structure shown in Figure 3 is closed at the end opposite the open side and, also as shown, this closed end of the structure is spaced from the open side several times the thickness of the wall itself; thus, in the unit there will be in at least three perpendicular directionsa considerable space behind the wall compared with that which will be found behind conventional wallbcards. In the tapered embodiment the container may be formed as'a conical or pyramidal bowl and in such case the requirement of having portions of the wall spaced several times the thickness of'the wall is fulfilled at any axial section which gives .the absorber unit the advantage of increased efiiciency for sound waves coming from any direction.

The containers may also be made of an outer shell 2: of rigid material which in itself is not sound absorbing, as shown in Figure 4, and through the walls of which the aperture 12 ex tends to the interior of the shell which then contains the porous sound absorbing material d, which in this embodiment is disposed on the interior surface of a rigid shell in form of a substantial uniform layer, leaving behind a chamber t as in Figure 3. Also the structure shown in Figure 4 is converging and has at its widest end an edge it which surrounds an open side of the casing. As in the case of Figure 3, also a section of the wall in this embodiment will be found conventional by those skilled in the art, representing another very common form of acoustic tile which has been in public use for many years. Also in the case of Figure 4. there are, at least at two perpendicular points in a plane parallelwith the open side, opposite portions of the wall spaced several times the thickness of the wall. This includes here the outer shell as well as the porous material, and opposite the open side aportion of the wall, the vertical bottom part as well as the adjacent lower portion of the converging walls, which is spaced from the open side several times the thickness of the wall;

With respect to the conventional construction of the wall itself, the embodiment of Figure 4 only differs from that shown in Figure 3 by the way the acoustic material, namely the porous sound absorbing material, is held in position. While in Figure 3 the sound absorbing material is self-supporting, this does not need to be the case in the embodiment shown in Figure 4, because here the rigid outer shell itself serves this purpose. In both cases the perforations or apertures have as their most important object to make the porous'material accessible to the sound waves which strike-the outer surface of the unit. From this it will be understood that neither the construction of the wall per se, nor the'mateshould-be substantially the same in at least'two' directions at right angles to each other. Preferably the units may have a circular or polygonal cross section. A converging or tapered form has the advantage of enabling an easy piling in a small space in view of packaging and shipment.

Th units are suspended in the way more specifically disclosed in Figures 3, i, 5 and 6. The casing structure has opposite the open side surrounded by the edge u an aperture or a hole :i through which extends one end of an elongated fastening element ,1, such as for instance a string adapted to hold the unit in the position shown with its edge u abutting against the surface e, to which purpose the fastening element f is connecteol at its other end to a point above the bottom of the unit, such as for instance a hook g on the surface e, as shown. The end of the fastening element which extends through the aperture 9' is secured to an element is which for instance may be disc-shaped, arranged outside the casing and extends across the aperture 7', engaging the structure at its exterior. I

As further shown in Figure 5, tension means, for instance a spring it, may be associated with the fastening element 1, to urge the edge u of the unit into abutment with the surface e.

The embodiment shown in Figure 6 only differs from those shown in Figures 3, 4 and 5 therein that the spring it is omitted and by another shape of the member is which is here formed like a plug having an inclined surface Z, so as to adjust itself automatically in a central position in the aperture 1.", when pushed upwardly along the strin 1 which extends-down through a central hole m in the plug. To enable fastening of the extending end of the string, the plug has a cylindrical groove 12 in which the excessive end-of the string can be wound up.

It will be understood that the shape of the units can be varied within the scope of the invention so that the containers may be barrel formed, as indicated in Fig. 7 in side view, which differs from the other embodiments thereby that the unit is freely suspended from the ceiling.

It will be understood that in the case of Figure '7 the unit may be composed of two oppositely arranged units of any of the constructions described above.

It will also be understood that the bowl-form of the containers as shown in the drawings may be varied within the scope of the invention-so that any bowl form may be used.

The units have special advantages in factory buildings where it will also be an advantage that they can be arranged under the ceiling in rows between the windows in cases where glass -ceiling is arranged.

Having thus described the invention, what i claim is:

1. In a sound absorbing unit, a wall structurev forming a hollow casing having an open side and surrounding an open sided chamber and having an exterior surface, a layer of sound absorbing material disposed within said chamber andad-.

jacent the wall structure and being porous for allowing the passage of sound waves and simultaneously damping the sound waves passingl therethrough, said wall structure having passages for sound waves to penetrate through said surface and into said porous layer, and bein so constructed and arranged that opposite wall portions in at least two perpendicular directions.

within a plane substantially parallel with said open side are spaced from each other acrosssaid,

chamber for a distance equalling at least a multiple of the thickness of said porous layer, an edge on said wall structure confining said open side, fastening means including a resilient tensioning element extending through said chamber from said open side, said element being shorter than said casing when in rest position, and means connected to said fastening means and coacting with a portion of said structure disposed opposite said open side for mounting said casing resiliently with said edge against the surface of an object.

2. In a sound absorbing unit, a wall structure forming a hollow casing having an open side and surrounding an open sided chamber and having an exterior surface, a layer of sound absorbing material disposed within said chamber and adjacent the wall structure and being porous for allowing the passage of sound waves and simultaneously damping the sound waves passing therethrough, said wall structure having passages for sound waves to penetrate through said surface and into said porous layer, and being so constructed and arranged that opposite wall portions in at least two perpendicular directions within a plane substantially parallel with said open side are spaced from each other across said chamber for a distance equalling at least a multiple of the thickness of said porous layer, an

edge on said wall structure confining said open side, fastening means extending substantially centrally through said chamber from said open side and including tensioning means, said tensioning means being shorter than said casing when in rest position, and means connected to said fastening means and coacting with a portion of said structure disposed opposite said open side for mounting said casing resiliently with said edge against the surface of an object.

OLAV E'BBESEN GRUE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,160,638 Bedell May 30, 1939 2,488,555 Pare Nov. 22, 1949 2,502,016 Olson Mar. 28, 1950 2,502,017 Beers Mar. 28, 1950 2,502,019 Olson Mar. 28, 1950 2,502,020 Olson Mar, 28, 1950 FOREIGN PATENTS Number Country Date 721,802 Germany July 22, 1942 

